Message Transfer Agents (MTAs) typically receive messages, store them, and forward them to the next server(s). In such cases, multiple high availability approaches may be deployed to ensure that such messages always exist on at least two servers in order to be resilient against hardware/software failures. Thus, a redundant message may be resubmitted for subsequent delivery to the intended recipient in a high availability system when a server is determined to be unavailable.
Without a distinction between network failures and server hardware/software failures, users may receive duplicate messages and unnecessary traffic due to subsequent deliveries of redundant messages may consume valuable system resources.